Electrochemical stack compression system

ABSTRACT

In accordance with one embodiment, an electrochemical cell stack compression system may include an integral, hollow frame configured to contain a plurality of electrochemical cells arranged along an axis in a stack configuration. The frame may have a defined shape and may form a continuous border around a periphery of the electrochemical cell stack when inserted. The frame may be formed of a plurality of fibers.

This patent application is a divisional of U.S. application Ser. No.14/198,317, filed Mar. 5, 2014, which claims the benefit of priorityunder 35 U.S.C. § 120 to U.S. Provisional Patent Application No.61/775,068, filed Mar. 8, 2013, which are incorporated herein byreference in their entirety.

Embodiments of the present disclosure relate to electrochemical cells,and more particularly, to systems for applying a compressive force tohigh differential pressure electrochemical cell stacks.

Electrochemical cells are used to generate an electric current fromchemical reactions. Electrochemical cell technology, like fuel cells andhydrogen compressors, offers a promising alternative to traditionalpower sources, such as fossil fuels, for a range of technologies,including, for example, transportation vehicles, portable powersupplies, and stationary power production. An electrochemical cellconverts the chemical energy of a proton source (e.g., hydrogen, naturalgas, methanol, gasoline, etc.) into electricity through a chemicalreaction with oxygen or another oxidizing agent. The chemical reactiontypically yields electricity, heat, and water.

A basic high differential pressure electrochemical cell comprises anegatively charged anode, a positively charged cathode, and anion-conducting material called an electrolyte. Different electrochemicalcell technologies utilize different electrolyte materials. A ProtonExchange Membrane (PEM) cell, for example, utilizes a polymeric,ion-conducting membrane as the electrolyte.

To generate electricity, a fuel, such as hydrogen gas, for example, maybe delivered to an anode side of an electrochemical cell. Here, hydrogenmay be split into positively charged protons and negatively chargedelectrons. The protons may then pass through an electrolyte membrane,such as a PEM, to a cathode side of the cell. The PEM may be configuredto allow only the positively charged protons to pass through to thecathode side of the cell. The negatively charged electrons may be forcedto pass through an external electric load circuit to reach the cathodeside of the cell, and in doing so, may generate a usable electricalcurrent. Oxygen may be delivered to the cathode side of the cell, whereit may react with the protons and the electrons to form water moleculesand heat as waste.

The cathode, electrolyte membrane, and anode of an individualelectrochemical cell, may collectively form a “membrane electrodeassembly” (MEA), which may be supported on both sides by bipolar plates.Gases, such as hydrogen and oxygen, may be supplied to the electrodes ofthe MEA through channels or grooves formed in the bipolar plates.

A single cell may generally produce a relatively small electricalpotential, about 0.2-1 volt, depending on the current. To increase thetotal voltage output, individual electrochemical cells may be stackedtogether, typically in series, to form an electrochemical cell stack.The number of individual cells in a stack may depend on the applicationand the amount of output required from the stack for that application.

The electrochemical cell stack may receive flows of hydrogen and oxygen,which may be distributed to the individual cells. Proper operation ofthe cell stack may require the maintenance of effective seals betweenthe individual cells, components of the cells, and flow conduits.Accordingly, the electrochemical cells in a stack may need to becompressed against one another to maintain sufficient electrical contactbetween the internal components of each cell. The amount of compressionbetween the cells may affect the contact resistance, electricalconduction, and membrane porosity, and thus may affect the overallperformance of the electrochemical cells. Accordingly, in order tomaintain contact between the cells and increase performance, uniformcompression is typically distributed over the electrochemical cellstack.

Often tie rods, bands, and/or springs may be used to apply compressiveforce to a cell stack. These compression mechanisms typically requirethe use of end plates located at both ends of the electrochemical cellstack. For example, end plates may cap each end of a cell stack, and tierods may extend from one end plate to the other, either external to thestack along the periphery, or within the stack by passing throughopenings in the cells of the stack. The tie rods may be tightened orloosened to move the end plates towards or away from each other toadjust the amount of compression exerted on the stack. In someinstances, bands may also be wrapped around the stack, stretching fromend plate to end plate, to maintain compression. To withstand thecompressive forces of tie rods and/or bands, thicker end plates and rodsmay be required to prevent bowing or cracking. This may increase thesize and weight of the cell stack, as well as the cost of theelectrochemical cell system. The problems of stack compression may befurther complicated in high-pressure electrochemical cell stacks,because high-pressure operation may cause increased separation of thecells. Thus, a cost-effective, compact, and lightweight system ofcompression is needed. Further, a system is needed that is capable ofmaintaining compression in an electrochemical cell stack over anextended period of time and under a range of operating conditions.

The present disclosure is directed toward the design of improvedcompression systems for use with electrochemical cells. In particular,the present disclosure is directed towards the design of adjustablecompression structures for use with electrochemical cells. Such devicesmay be used in electrochemical cells operating under high differentialpressures, including, but not limited to hydrogen compressors, fuelcells, electrolysis cells, hydrogen purifiers, and hydrogen expanders.

Embodiments of the present disclosure are directed to a system forapplying compressive force to electrochemical cell stacks.

In accordance with one embodiment, an electrochemical cell stackcompression system may include an integral, hollow frame configured tocontain a plurality of electrochemical cells arranged along an axis in astack configuration, wherein the frame has a defined shape and forms acontinuous border around a periphery of the electrochemical cell stackwhen inserted, and wherein the frame is formed of a plurality of fibers.

Various embodiments of the disclosure may include one or more of thefollowing aspects: the frame may be formed of a plurality of fiberscomposed of different materials; the frame may include multiple layersformed of fibers; the frame may include a friction-reducing layerlocated between at least one of the multiple layers formed of fibers;the frame may include at least two opposing wall surfaces; the frame maybe further configured to contain at least one end block located at anend region of the frame; the frame may be further configured to containat least one compression mechanism configured to apply a compressiveforce to the electrochemical cell stack; the compression mechanism mayinclude at least one gib; the compression mechanism may be configured toexpand when heated; the compression mechanism may include one or moreinternal drive screws extending between two separate portions, whereinrotating the internal drive screws in one direction moves the twoportions further away from each other and rotating the internal drivescrews in the opposite direction moves the two portions closer to eachother; and the frame may be configured to accommodate multiple differentsizes of electrochemical cell stacks.

In accordance with another embodiment, an electrochemical stackcompression system may include a structure having a defined shape thatis configured to receive and contain a plurality of electrochemicalcells arranged in a series along an axis to form an electrochemicalstack and at least one compression mechanism configured to apply acompressive force to the electrochemical stack located adjacent to andalong the axis of the electrochemical stack, wherein the structure formsa continuous border surrounding the electrochemical stack and the atleast one compression mechanism when contained.

Various embodiments of the disclosure may include one or more of thefollowing aspects: the compression mechanism may include at least onegib; the compression mechanism may include a block that is configured toexpand in response to an increase in temperature; the compressionmechanism may include internal drive screws configured to increase thesize of the compression mechanism when the internal drive screws arerotated in a first direction and to decrease the size of the compressionmechanism when the internal drive screws are rotated in a seconddirection opposite the first direction; the structure may be formed ofwound fibers; the fibers may be non-conductive; the fibers may becarbon; and a height of the structure along the axis of theelectrochemical stack may change in response to a load applied by thecompression mechanism to the electrochemical stack when receiving thecompression mechanism.

A method of preloading various embodiments of the disclosure may includeinserting the electrochemical stack into the structure, inserting the atleast one compression mechanism into the structure, configuring thecompression mechanism to apply a predetermined load within thecompression system, and measuring a change in height of the structurealong the axis of the electrochemical stack to determine the load beingapplied by the compression mechanism.

Various embodiments of the method may further include: inserting atleast one end block into the structure; the compression mechanism mayinclude two gibs and configuring the compression mechanism may includewedging the two gibs against each other; configuring the compressionmechanism may include increasing the temperature of the compressionsystem to expand the compression mechanism; and configuring thecompression mechanism includes rotating a plurality of internal drivescrews to expand the compression mechanism.

In accordance with another embodiment of the present disclosure, anelectrochemical stack compression system may include an integral, hollowstructure having a defined shape and formed of a plurality of woundfibers; a plurality of electrochemical cells arranged in a series alongan axis to form an electrochemical stack, wherein the electrochemicalstack is contained within the structure; at least one end blockcontained within the structure and located at an end region of thestructure; and at least one compression mechanism contained within thestructure, wherein the at least one compression mechanism is configuredto apply a compressive force to the electrochemical stack, and whereinthe electrochemical stack, the at least one end block, and the at leastone compression mechanism are contained in series within the structuresuch that the structure forms a continuous border around and adjacent toa periphery of the electrochemical stack, the at least one end block,and the at least one compression mechanism.

Various embodiments of the disclosure may include one or more of thefollowing aspects: the fibers may be configured to stretch and contractin response to changes in the compressive force; the at least onecompression mechanism may include a gib; and the at least onecompression mechanism may be configured to expand.

Additional objects and advantages of the embodiments will be set forthin part in the description that follows, and in part will be obviousfrom the description, or may be learned by practice of the embodiments.The objects and advantages of the embodiments will be realized andattained by means of the elements and combinations particularly pointedout in the appended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the disclosure,and together with the description, serve to explain the principles ofthe disclosure.

FIG. 1 illustrates an exploded view of an exemplary electrochemicalcell, according to an embodiment of the present disclosure.

FIG. 2A illustrates an exemplary electrochemical cell compressionsystem, according to an embodiment of the present disclosure.

FIG. 2B illustrates an exemplary electrochemical cell compressionsystem, according to an embodiment of the present disclosure.

FIG. 2C illustrates a cross-section of the exemplary electrochemicalcell compression system of FIG. 2A.

FIG. 3A illustrates an exemplary compression mechanism for anelectrochemical cell compression system according to an exemplaryembodiment of the present disclosure.

FIG. 3B illustrates an alternative view of the exemplary compressionmechanism of FIG. 3A.

FIG. 4 illustrates an exemplary compression mechanism for anelectrochemical cell compression system according to an exemplaryembodiment of the present disclosure.

Reference will now be made in detail to the exemplary embodiments of thepresent disclosure described below and illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to same or like parts.

While the present disclosure is described herein with reference toillustrative embodiments of a PEM electrochemical cell employinghydrogen, oxygen, and water, it is understood that the devices andmethods of the present disclosure may be employed with various types ofelectrochemical cells, including, but not limited to hydrogencompressors, fuel cells, electrolysis cells, hydrogen purifiers, andhydrogen expanders. Those having ordinary skill in the art and access tothe teachings provided herein will recognize additional modifications,applications, embodiments, and substitution of equivalents that all fallwithin the scope of the disclosure. Accordingly, the disclosure is notto be considered as limited by the foregoing or following descriptions.

Other features and advantages and potential uses of the presentdisclosure will become apparent to someone skilled in the art from thefollowing description of the disclosure, which refers to theaccompanying drawings.

FIG. 1 depicts an individual electrochemical cell 10, according to anembodiment of the present disclosure. In the exploded side view shown inFIG. 1, cell 10 includes a central, electrolyte membrane 8. Electrolytemembrane 8 may be positioned between an anode 7A and a cathode 7B.Together, electrolyte membrane 8, anode 7A, and cathode 7B may form MEA3. Hydrogen atoms supplied to anode 7A may be electrochemically splitinto electrons and protons. The electrons may flow through an electriccircuit (not shown) to cathode 7B, generating electricity in theprocess, while the protons may pass through electrolyte membrane 8 tocathode 7B. At cathode 7B, protons may react with electrons and oxygensupplied to cathode 7B to produce water and heat.

Electrolyte membrane 8 may electrically insulate anode 7A from cathode7B. Electrolyte membrane 8 may be any suitable membrane, including,e.g., a PEM membrane. Electrolyte membrane 8 may be formed of a purepolymer membrane or a composite membrane, which may include, e.g.,silica, heteropolyacids, layered metal phosphates, phosphates, andzirconium phosphates, embedded in a polymer matrix. Electrolyte membrane8 may be permeable to protons but may not conduct electrons. Anode 7Aand cathode 7B may include porous carbon electrodes containing acatalyst. The catalyst material, e.g., platinum or any other suitablematerial, may speed up the reaction of oxygen and fuel.

The size and shape of MEA 3 may be increased or decreased depending onthe application of cell 10 and the given load requirements. For example,the thickness, length, or width of MEA 3 may be adjusted according tothe given application and requirements. Additionally, the concentrationof catalyst material in anode 7A and cathode 7B may be adjustedaccording to the given application. The concentration of catalystmaterial in anode 7A and cathode 7B and the thickness of electrolytemembrane 8 may each affect the total thickness of MEA 3.

In some embodiments, electrochemical cell 10 may optionally include oneor more electrically conductive flow structures 5 on each side of MEA 3.Flow structures 5 may serve as diffusion media enabling the transport ofgases and liquids within cell 10. Flow structures 5 may also promoteelectrical conduction, aid in the removal of heat and water fromelectrochemical cell 10, and provide mechanical support to electrolytemembrane 8. Flow structures 5 may include, e.g., flow fields, gasdiffusion layers (GDL), or any suitable combination thereof. Flowstructures 5 may be formed of “frit”-type sintered metals, layeredstructures, e.g., screen packs and expanded metals, andthree-dimensional porous substrates. An exemplary porous metallicsubstrate may consist of two distinct layers having different averagepore sizes. Such flow structures 5 may be formed of any suitablematerial, including, e.g., metals or metal alloys, such as, e.g.,stainless steel, titanium, aluminum, nickel, iron, and nickel-chromealloys, or any combination thereof. In addition, flow structures 5 mayinclude a suitable coating, such as a corrosion-resistant coating, likecarbon, gold, or titanium-nitride.

The reactant gases on each side of the electrolyte membrane are oftenpresent at different pressures, e.g., operating pressures may range fromapproximately 0 psid to 15,000 psid, creating a pressure differentialacross MEA 3. For example, when an electrochemical cell is configured asa hydrogen compressor, the flow structure on the cathode side of themembrane is exposed to higher pressures than the flow structure on theanode side. The pressure differential may create a force on MEA 3 thatcauses MEA 3 to move away from the high pressure side toward the lowpressure side. This movement may cause a reduction in contact pressureand separation of the contacting surface of MEA 3 from flow structures 5on the high-pressure side. Reduction in pressure and subsequentseparation between the contacting surfaces of MEA 3 and high-pressureflow structures 5 may reduce the electrical conduction and increase thecontact resistance between the two, reducing the efficiency ofelectrochemical cell 10.

Flanking flow structures 5 and MEA 3, cell 10 may also include twobipolar plates 2A, 2B. Bipolar plate 2A may be positioned on thehigh-pressure side, and bipolar plate 2B may be positioned on thelow-pressure side of electrochemical cell 10. Bipolar plates 2A, 2B mayseparate cell 10 from neighboring electrochemical cells (not shown) in astack. In some embodiments, two adjacent cells in an electrochemicalcell stack may share a common bipolar plate.

Bipolar plates 2A, 2B may act as current collectors, may provide accesschannels for the fuel and the oxidant to reach the respective electrodesurfaces, and may provide channels for the removal of water formedduring operation of electrochemical cell 10 by means of exhaust gas.Bipolar plates 2A, 2B may also provide access channels for coolingfluid, such as, e.g., water, glycol, or a combination thereof. Bipolarplates 2A, 2B may be made from aluminum, steel, stainless steel,titanium, copper, nickel-chrome alloy, graphite, or any other suitableelectrically conductive material or combination of materials.

FIGS. 2A through 2C show exemplary electrochemical cell stackcompression systems 20, according to embodiments of the presentdisclosure. Each individual cell 10 may be stacked within compressionsystem 20 to form an electrochemical cell stack 11. Stack 11 may becomprised of any suitable number of cells 10. Stack 11 may be locatedbetween end blocks 12A and 12B, which may be located at each end ofstack 11. End blocks 12A, 12B may be formed of any suitable metal,plastic, or ceramic material having adequate compressive strength, e.g.,aluminum, steel, stainless steel, cast iron, titanium, polyvinylchloride, polyethylene, polypropylene, nylon, polyether ether ketone,alumina, or any combination thereof.

Stack 11 and end blocks 12A, 12B may be housed in a structure 15. Awound fiber structure 15 may provide a resilient frame capable ofhousing a high-pressure electrochemical cell stack without significantlyincreasing the weight or size of the electrochemical cell system.Structure 15 may form a frame with a defined shape into which stack 11and end blocks 12A, 12B are positioned. FIG. 2A depicts an elongated,rounded, structure 15, but structure 15 may be any suitable shape,including, e.g., rectangular, oval, circular, or square. The walls ofstructure 15 may form a continuous border long the periphery of stack 11and end blocks 12A, 12B, and structure 15 and may or may not enclose thefront and/or back portions of stack 11 and end blocks 12A, 12B. Endbocks 12A, 12B, stack 11, and any other components housed in structure15 may be configured to lie flush with the walls of structure 15 on anopen face, or the components may be recessed within structure 15 or theymay protrude from structure 15, or any suitable combination thereof.

Structure 15 may be dimensioned to house end blocks 12A, 12B and stack11, which may include any suitable number of electrochemical cells 10.In some embodiments, the size, e.g., the height H, length L (shown inFIG. 2C), and/or width, of structure 15 may vary, for example, structure15 may be configured to stretch during pre-loading, as discussed furtherbelow. Structure 15 may be dimensioned so as to snugly fit the desiredcontents, for example, electrochemical stack 11 and end blocks 12A, 12B,so as to not substantially increase the size of the overallelectrochemical cell system.

In some embodiments, structure 15 may be formed of wound fibers that arecapable of stretching and contracting. For example, structure 15 may beformed of wound fibers, such as, e.g., carbon, glass, or aramid (e.g.,KEVLAR®) fibers. The fibers may be non-conductive to reduce thelikelihood of short-circuiting stack 11. In some embodiments, structure15 may be formed of metallic fibers, such as, e.g., steel, stainlesssteel, or aluminum, or alloys, such as Inconel. Structure 15 may beformed of homogenous fibers or a mixture of different fibers.Additionally, structure 15 may be formed with or without an epoxy matrixor other suitable material to bind the fibers together. As is shown inFIG. 2C, the walls of structure 15 may have a thickness ct.' The woundfiber material properties, such as, e.g., tensile strength, and wallthickness t may be selected to achieve a desired compressive force onstack 11. The fibers making up structure 15 may be wound together toform one integral frame unit into which stack 11 and various othercomponents fit.

In some embodiments, such as the one shown in FIG. 2B, structure 15 maybe formed of multiple layers 13A, 13B, and 13C. Though FIG. 2B depicts 3layers, multi-layered embodiments of structure 15 may include anysuitable number of layers. Each layer may be formed of homogenous fibersor of a combination of different fibers. The layers may be attached toone another, via, e.g., bonding or fastening mechanisms, or may beunattached and held together through, e.g., friction. Additionally, somelayers may be attached while other layers may be unattached. In themulti-layer embodiments, structure 15 may include one or moreslip-planes 4 between the layers. Slip-plane 4 may be formed of aseparate layer or of a coating on one of the layers, such as, e.g., apolytetrafluoroethylene (e.g., TEFLON®), polyetheretherketone,polyimide, nylon, polyethylene, or polymer layer or coating, or anyother suitable friction-reducing material to decrease the frictionbetween the layers. If incorporated, slip-plane 4 may be includedbetween each layer or may be included between fewer than all of thelayers. The inclusion of slip-plane 4 may reduce the amount of stresswithin structure 15 and compression system 20, particularly inembodiments having thicker structure walls.

In some embodiments, end blocks 12A, 12B may be also be configured tofit into structure 15 so that one or both of end blocks 12A, 12B maymove within structure 15. For example, end blocks 12A, 12B may beallowed to slip along the walls of structure 15. This configuration maydecrease the stress in structure 15, which may in turn allow forstructure 15 to incorporate thinner walls. In such embodiments, endblocks 12A, 12B may include a suitable friction reducing material orcoating, e.g., polytetrafluoroethylene (e.g., TEFLON®),polyetheretherketone, polyimide, nylon, polyethylene. In otherembodiments, end blocks 12A, 12B may be attached to the walls ofstructure 15 or may be otherwise configured so that end blocks 12A, 12Bmay not slip once inserted into structure 15.

According to another aspect of the disclosure, compression system 20 mayinclude one or more gibs to promote uniform compression ofelectrochemical stack 11 within structure 15. The gibs may act as awedge to drive two parallel planes in structure 15 apart as the gibs arewedged together in a direction perpendicular to the two parallel planes.For example, as shown in FIGS. 2A through 2C, gibs 14A, 14B may beinserted between electrochemical cell stack 11 and end block 12A todrive stack 11 and end block 12A apart while maintaining their parallelorientation. Gib 14B may have a flat surface and an opposite, angledsurface. Gib 14B may be inserted into structure 15 so that the flatsurface lies adjacent to stack 11 and the angled surface faces upwards.Gib 14B may be oriented so that the upward-facing, angled surface slopesin a downward direction toward the front face of structure 15 beingloaded. Gib 14A may then be inserted next to gib 14B, and the two gibsmay be driven together. Gib 14A may also have a flat surface and anopposite, angled surface sloped at an angle complimentary to the slopedsurface of gib 14B. The angled surface of gib 14A may be insertedadjacent the angled surface of gib 14B so that the angled surface alsoslopes in downward direction towards the front face of structure 15.Thus, as gib 14A is inserted into structure 15 and driven against 14B,the complimentary slopes may slide against each other, pushing the flatsurfaces of gibs 14A, 14B further apart from each other and towards endblock 12A and stack 11. Gib 14A may be inserted into structure 15 untila desired compressive force is exerted on stack 11.

Gib 14B may also include a grip portion configured to aid in theinsertion and removal of gibs 14A, 14B from structure 15. In someembodiments, gib 14B may include one or more gripping mechanismconfigured to engage the walls of structure 15 to reduce movement of gib14B as gib 14A is inserted. The gripping mechanisms of gib 14B mayengage an inner surface of structure 15 or may extend from gib 14B andengage an edge and/or outer surface of structure 15. For example, FIG.2A depicts hooks 9 protruding outwards from gib 14B and engaging theedges of opposite walls of structure 15. Hooks 9 may prevent gib 14Bfrom sliding further into structure 15 as gib 14A is inserted. Gib 14Bmay include any suitable gripping mechanism or combination of grippingmechanisms, such as, e.g., protrusions like pegs or hooks, or texturedsurfaces to reduce movement as gib 14A is wedged against gib 14B. Thegripping mechanisms may be any suitable size, shape, and orientation. Insome embodiments, the thick end of gib 14B may be constrained against afixed surface as gib 14A is driven, preventing translation against cellstack 11.

While two gibs 14A, 14B are depicted, any suitable number of gibs may beincluded in compression system 20. Additionally, gibs 14A, 14B may beincluded in any suitable position, for example, gibs 14A, 14B may bepositioned between stack 11 and end block 12B, or sets of gibs may belocated on either side of stack 11.

Gibs 14A, 14B may be formed of any suitable material, such as, e.g.,steel, stainless steel, ceramic, or aluminum. Gibs 14A, 14B may alsohave any suitable coating, such as a lubricant, to reduce galling or tofacilitate insertion into compression system 20. Such a suitablefriction reducing material may include, e.g., polytetrafluoroethylene(e.g., TEFLON®), polyetheretherketone, polyimide, nylon, polyethylene,or other lubricious polymer coatings, or any other suitable material.

Gibs 14A, 14B may be any suitable shape and size for insertion intostructure 15. For example, in some embodiments, the size and shape ofgibs 14A, 14B may at least in part reflect the size and shape of theinterior region of structure 15. Gibs 14A, 14B may be designed with anysuitable angle. The angle that gibs 14A, 14B are designed with may bebased, at least in part, on the required pre-load of stack 11, which maybe based on the application of stack 11 and the accompanying outputrequirements. The size and shape of gibs 14A, 14B may also be based, inpart, on the size of stack 11 compared to the size of structure 15. Forexample, the same size structure 15 may be used to house stacks 11 ofdifferent sizes. Thus, larger gibs 14A, 14B may be used with smallerstacks 11 to apply an appropriate compressive force, and vice versa.

Gibs 14A, 14B may be used to apply compression to stack 11, maintain auniform load, stabilize system 20, and provide planarity. Duringassembly, components of compression system 20, such as stack 11 and endblocks 12A, 12B may be inserted into structure 15. At this time,structure 15 may be “pre-loaded” or pre-stretched to apply apredetermined compressive force to stack 11 in order to maintain contactbetween electrochemical cells 10. This may be accomplished usingcompressive mechanisms, such as gibs 14A, 14B. Once the other componentsare inserted, gibs 14A, 14B may be inserted into structure 15 to fillany gaps. Gibs 14A, 14B may be wedged against each other until theirparallel surfaces are forced apart far enough to achieve a desiredcompressive load on the surrounding components, e.g., stack 11, withinstructure 15. As gibs 14A, 14B are driven together during pre-loading,tension within the walls of wound fiber structure 15 may increase, andthe fibers may stretch. This may increase the height H of structure 15.The amount of expansion of structure 15 may depend, at least in part, onthe wall thickness t and the types of fibers that make up structure 15.Measuring the change in height H of structure 15 during pre-loading mayindicate the compressive force being applied to stack 11 and may allowfor more precise control of pre-loading conditions. Thus, when woundfiber structure 15 is used in conjunction with the disclosed compressionmechanisms, system 20 may provide a lightweight, low-cost system foraccurately and effectively applying a compressive load to stack 11.

During operation, as gas pressure in the stack increases, thecompressive loading on stack 11 may decrease until cells 10 separate. Atthis point, structure 15 may begin to stretch more than its pre-loadedvalue. Thus, if stack 11 heats up more than structure 15 duringoperation, structure 15 may be forced to stretch more than thepre-loaded value due to differential thermal expansion and the forceapplied to the stack will increase. Thus, the materials of structure 15and any compressive mechanisms may be selected based on their thermalproperties to reduce the potential for loss of compressive force duringoperation.

In some embodiments, system 20 may include other compressive mechanismsinstead of, or in addition to, gibs 14A, 14B. For example, as is shownin FIGS. 3A and 3B, in some embodiments, one or more thermal expansionblocks 21 may be used to apply compression to stack 11. Block 21 may becooled to a temperature below that of stack 11. During pre-loading,cooled block 21 may be inserted into compression system 20. As thetemperature of block 21 increases inside of structure 15, block 21 mayexpand, and accordingly, may apply compression to stack 11. Block 21 maybe formed of any material or combination of materials having suitablethermal expansion characteristics, such as, e.g., suitable metals, metalalloys, or ceramics. In some embodiments, block 21 may be formed ofmaterials with a higher coefficient of thermal expansion than that ofstructure 15. In such embodiments, as stack 11 and block 21 are broughtup to operating temperature (generally between 30 and 100° C.), block 21may expand more than structure 15. Such expansion may result incompressive loading of stack 11.

One advantage of thermally activated compression mechanisms is thatblock 21 may be easier to insert into structure 15. Inserting block 21prior to thermal expansion may reduce the wear and stress on thesurrounding components of compression system 20. For example, as isshown in FIG. 3A, when block 21 is initially inserted duringpre-loading, a gap 17 may exist in compression system 20. As block 21warms, gap 17 may disappear as block 21 expands and fills thesurrounding space (shown in FIG. 3B). Once gap 17 disappears, thecontinued expansion of block 21 may begin to compress stack 11 and applya compressive load. The thermal properties of block 21 may be chosen toimpart a desired compressive load based on the size of stack 11 and thesize of gap 17 in structure 15. It will be understood that while gap 17is shown between inserted block 21 and end block 12A, block 21 may beoriented so that gap 17 occurs on either side of block 21, or on bothsides of block 21. Further, gap 17 may occur in any region withinstructure 15.

While block 21 is herein described as the expansion member, one or moreof end blocks 12A or 12B may be designed to provide thermal compressioninstead of, or in addition to, block 21. Further, gibs 14A, 14B may alsobe made of suitable material to allow them to apply compression via useas a wedge as well as through thermal expansion. Additionally, multiplethermal expansion blocks 21 may be used, or a combination of thermalexpansion block 21 and gibs 14A, 14B may be inserted into structure 15.

Other embodiments of the present disclosure may include still othercompression mechanisms. As shown in FIG. 4, a screw compression unit 19with internal drive screws may be used to apply a compressive load.Compression unit 19 may be configured to be removable from structure 15or may be attached to structure 15. As is shown in FIG. 4, threadedscrews 18 may extend from a base 16B of compression unit 19. Theopposite ends of screws 18 may extend into complimentary threaded inlets(not shown) in block 16A of compression unit 19. Rotating screws 18 inone direction may cause screws 18 to screw further into the threadedinlets in block 16A, moving block 16A closer to base 16B and decreasingthe gap between 16A and 16B. Decreasing the gap between 16A and 16B mayreduce the compressive force applied to stack 11. Rotating screws 18 inthe opposite direction may cause screws 18 to unscrew from the threadedinlets in block 16A, moving block 16A away from base 16B and increasingthe gap between 16A and 16B. Increasing the gap between 16A and 16B mayincrease the compressive force applied to stack 11. During pre-loading,compression unit 19 may be inserted into structure 15 while there islittle or no gap between block 16A and base 16B. Once inserted, screws18 may be rotated so as to increase the gap between block 16A and base16B in order to apply a desired compressive force to stack 11.

While four screws 18 are depicted in FIG. 4, any suitable number ofthreaded components may be included in compression unit 19.Additionally, the threaded components may be distributed on base 16B inany suitable arrangement. Screws 18 may be any suitable shape or sizeand may be formed of any suitable material, for example, any metal,metal alloy, or ceramic. Any number of compression units 19 may beincorporated in system 20, and compression unit 19 may be used in placeof or in addition to either or both of gibs 14A, 14B and thermalexpansion block 21. Further, in some embodiments, compression unit 19may also be incorporated into one of the components or compressionmechanisms described previously. For example, one or more of end blocks12A, 12B, gibs 14A, 14B, or block 21 may include internal drive screws.

One additional advantage of some of the embodiments of disclosedcompression system 20 (aside from the reduction in overall stack sizeand weight) is that compression system 20 may accommodateelectrochemical stacks of different sizes. By incorporating gibs 14A,14B, thermal expansion block 21, and/or compression unit 19, structure15 may be configured to receive electrochemical cell stacks of differentsizes with different numbers of electrochemical cells suitable fordifferent applications and output levels. If a smaller stack 11 withfewer electrochemical cells 10 is contained in structure 15, then largercompression mechanisms or a larger number of or combination ofcompression mechanisms may be inserted around stack 11 duringpre-loading to fill any additional space and apply a desired compressiveforce. Alternatively, if a larger electrochemical cell stack 11 withmore cells 10 is housed in structure 15, smaller compression mechanismsor fewer compression mechanisms may be inserted around stack 11.Accordingly, the same basic structure 15 may be capable of housingdifferent sized electrochemical cell stacks appropriate for differentapplications and different output levels. This may reduce manufacturingcosts, because one standard structure 15 may be produced for housing avariety of electrochemical cell stack sizes suitable for a variety ofapplications. Thus, the same basic technology may produce structures forstacks of various cell counts and sizes. By incorporating differentnumbers of or different types of compression mechanisms described above,the same structure 15 may be capable of accommodating a range ofoperating conditions over an extended period of time.

Additionally, the wall thickness of structure 15 and the types of fibersselected to form structure 15 may allow structure 15 to accommodate arange of electrochemical cell stack sizes. Further, in multi-layerembodiments of structure 15, structure 15 may be configured so that oneor more of the layers is removable or separable from the other layers.For example, one or more of the layers may be nested within anotherlayer and may be capable of being completely removed from thesurrounding layer. In an embodiment like that shown in FIG. 2B, layer13A may be nested within and removable from layer 13B, for example, andslip-plane 4 may facilitate removal. Depending on the size ofelectrochemical cell stack 11 to be inserted into structure 15, one ormore layers may be removed to adapt structure 15 to the currentlyapplicable operating conditions.

Application of embodiments described above may improve performance ofelectrochemical cells, including electrochemical cells operating underhigh-pressure conditions.

The many features and advantages of the present disclosure are apparentfrom the detailed specification, and thus, it is intended by theappended claims to cover all such features and advantages of the presentdisclosure that fall within the true spirit and scope of the presentdisclosure. Further, since numerous modifications and variations willreadily occur to those skilled in the art, it is not desired to limitthe present disclosure to the exact construction and operationillustrated and described, and accordingly, all suitable modificationsand equivalents may be resorted to, falling within the scope of thepresent disclosure.

Moreover, those skilled in the art will appreciate that the conceptionupon which this disclosure is based may readily be used as a basis fordesigning other structures, methods, and systems for carrying out theseveral purposes of the present disclosure. Accordingly, the claims arenot to be considered as limited by the foregoing description.

What is claimed is:
 1. An electrochemical stack compression systemcomprising: a structure having a defined shape that is configured toreceive and contain: a plurality of electrochemical cells arranged in aseries along an axis to form an electrochemical stack; and at least onecompression mechanism configured to apply a compressive force to theelectrochemical stack, wherein the compression mechanism is locatedadjacent to and along the axis of the electrochemical stack; wherein thestructure forms a continuous border surrounding the electrochemicalstack and the at least one compression mechanism when contained.
 2. Thecompression system of claim 1, wherein the compression mechanismincludes a first gib and a second gib inserted between the stack and anend block, the first and second gibs each having a flat surface and anopposite, angled surface, the flat surface of the first gib liesadjacent the stack, and the angled surface of the second gib is slopedat an angle complimentary to the angled surface of the first gib and isinserted adjacent the angled surface of the first gib.
 3. Thecompression system of claim 1, wherein the compression mechanismincludes internal drive screws configured to increase the size of thecompression mechanism when the internal drive screws are rotated in afirst direction and to decrease the size of the compression mechanismwhen the internal drive screws are rotated in a second directionopposite the first direction.
 4. The compression system of claim 1,wherein the structure is formed of wound fibers constructed of aplurality of discrete layers.
 5. The compression system of claim 4,wherein each discrete layer is formed of homogenous fibers.
 6. Thecompression system of claim 4, wherein each discrete layer is formed ofa combination of fibers of different materials.
 7. The compressionsystem of claim 4, wherein at least two of the discrete layers areattached by bonding or fastening mechanisms.
 8. The compression systemof claim 4, wherein at least two of the discrete layers are unattachedand held in position by fiction.
 9. The compression system of claim 4,wherein the frame includes a friction-reducing layer located between atleast two of the discrete layers.
 10. The compression system of claim 4,wherein at least a portion of the wound fibers are carbon fibers. 11.The compression system of claim 4, wherein the fibers arenon-conductive.
 12. The compression system of claim 1, wherein thestructure has two opposing walls connected by rounded circular ends. 13.The compression system of claim 12, wherein the end block has a roundedsurface configured to abut one of the rounded circular ends of thestructure.
 14. The compression system of claim 1, wherein a height ofthe structure along the axis of the electrochemical stack changes inresponse to a load applied by the compression mechanism to theelectrochemical stack when containing the compression mechanism.
 15. Amethod of pre-loading the compression system of claim 1, the methodcomprising: inserting the electrochemical stack into the structure;inserting the at least one compression mechanism into the structure;configuring the compression mechanism to apply a predetermined loadwithin the compression system; and measuring a change in height of thestructure along the axis of the electrochemical stack to determine theload being applied by the compression mechanism.
 16. The method of claim15, wherein the compression mechanism configuring the compressionmechanism includes at least one of wedging the first gib against thesecond gib, increasing the temperature of the compression system toexpand the compression mechanism, or rotating a plurality of internaldrive screws to expand the compression mechanism.